Old-Exam. Selected-Questions-Ch.#17-082 (Dr. Naqvi-Phys-102.04-06)
T081: Q5.A pipe has two consecutive resonance frequencies of 600 Hz and 1000 Hz. One end of the pipe is closed. What is the fundamental frequency of the pipe? (Ans: 200 Hz)
Q6.The intensity of sound emitted by a source is doubled. What is the change in intensity level of the sound? (Ans: 3.0 dB)
Q7.Two identical loudspeakers, facing each other, are in phase and each has a frequency of 85 Hz. A man at the midpoint between the two loudspeakers moves slowly toward one of them until he hears the first minimum in sound. How far did he move? (The speed of sound in air = 340 m/s) (Ans: 1.0 m)
Q8.If it were possible for a man to move with the speed of sound directly toward a stationary whistle emitting a sound of frequency f, he would hear (Ans: a sound of frequency 2f)
T072: Q6.Two speakers S1 and S2 are placed on the y-axis as shown in figure 1. The speakers are in phase and emit identical sound waves with a given frequency. An observer, standing at point A, hears a sound of maximum intensity. As the observer moves along a straight line parallel to the y-axis and reaches point B, he hears first minimum of sound intensity. The frequency of sound emitted by the speakers is? (speed of sound in air = 343 m/s). (Ans: 121 Hz)
Q7. A stationary train passenger hears a frequency of 520 Hz as a train approaches a bell on a trackside safety gate. After the train passes the gate the passenger hears a frequency of 480 Hz for the bell sound. The speed of the train is : ( speed of sound in air = 343 m/s) (Ans: 13.7 m/s)
T071:Q#5. In the figure below, two speakers are driven by the same generator and are a distance of 1.0 m apart. The speakers emit sound waves at a frequency of 686 Hz that are in phase. A listener starts at A and moves toward B. What will be the distance from A of the first point at which he will observe constructive interference? The speed of sound in air is 343 m/s. (Ans: 0.25 m)
T062:Q7. The intensity of a sound wave of frequency 360 Hz is 1.6×10-6 W/m2. .If the speed of sound in air is 343 m/s, what is the displacement amplitude of the air molecules oscillation caused by this wave? (ρair=1.21 kg.m3) (Ans:3.88×10-8 m )
Q8. A person is listening to sounds from two different sources simultaneously. One source has sound level of 80 dB, while the other has 90 dB. What combined sound level will the person hear? (Ans: 90.4 dB)
T061: Q#5. Sound waves of frequency 340 Hz are sent into the top of a vertical tube containing water, as shown in the figure 1. If standing waves are produced, as shown, what is the height level of the water?. [Speed of sound in air = 340 m/s] (Ans: 35 m)
Q#6. A man strikes one end of a long steel pipe of length L, filled with water, by a hammer. A detector attached to the other end of the pipe receives two sounds signals, one from the wave that travels through the pipe and the other from the wave that travels through the water. If the time difference between the two wave signals is 0.02 s, what is the length of the pipe? (Speeds of sound in steel and water are Vs = 5940 m/s and Vw = 1480 m/s, respectively). (Ans:39 m)
T052: Q#1. A pipe open at both ends has a fundamental frequency of 400 Hz. What will be the fundamental frequency if the pipe is closed at one end? (speed of sound is 340 m/s) (Ans: 200 Hz.)
Fig. 1, T072 Fig. 1, T071 Fig. 1, T061 Fig. 1, T032
T051: Q#6. The maximum pressure amplitude ΔPm that the human ear can tolerate is about 30 N/m2. If the maximum displacement Sm is 1.3*10-5 m, find the frequency of the corresponding sound. (ρ =1.2 kg/m3, the speed of sound =340 m/s). (Ans: 900 Hz)
T042:Q#5: In a liquid having density 1.30*10**3 kg/m**3, longitudinal waves with frequency of 400 Hz are found to have a wavelength of 8.0 m. Calculate the bulk modulus of the liquid. [A1 1.33*10**10 Pa.}
T041:Q#1: Two pipes have the same length L. Pipe B open at one end and closed at the other, while pipe A open both ends. Which harmonic of pipe B matches the second harmonic of pipe A? (Ans: Never match).
T032:Q#6: Two transmitters, S1 and S2 shown in figure (1), emit identical sound waves of wavelength lambda. The transmitters are separated by a distance lambda/2. Consider a big circle of radius R with its center halfway between these transmitters. How many interference maxima are there on this big circle? (Ans: 2.)
Q10) Organ pipe A, with both ends open, has a fundamental frequency of 340 Hz and length 0.4 m. The third harmonic of organ pipe B, with one end open, has the same frequency as the second harmonic of pipe A. How long is pipe B? (Ans: 0.3 m.)
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